Big Blue's HVAC Blower Issues

[Gary Lewis]

My father used to say "Ain't that a revolting development."  I used to think I understood, but as of this morning I HAVE IT!  

After the conversation with René yesterday I thought I'd test Big Blue's HVAC blower motor.  The plan was to take it out and oil it and then see what difference that made.

But it dawned on me that I might want to take some benchmark measurements first to see if I'd made any improvements.  However, when I did I was dismayed, or maybe revolted, by the results.  Here's what I got as well as some calc's to go with it using the as-is harness in the truck:

Test 1: Battery @ 12.5V, positive terminal to motor @ 11.15v, negative terminal @ 3.2v, and current @ 10.2 amps.  WOW!  Effective voltage to the motor is only 9.3v???  That's only 74%!  And 95 watts.

Test 2: Battery @ 12.8v, voltage to motor @ 8.4v, and current @ 8.6A for 72 watts

Test 3: Battery at 13.7v, voltage to motor @ 8.5v, and current @ 8.6A for 73 watts

Note that some of the differences in the readings might be due to having introduced a different meter to read battery voltage, and directly reading voltage to the motor instead of reading the negative side and then the positive side.  But nevertheless, there are PROBLEMS!  And I thought I had that covered, at least on the negative side, with a relay.  

But then I wondered what would happen if I jumpered the motor directly to the battery using the light test jumpers I have, which might be 18 gauge.  And here are those results:

Test A: Battery @ 13.0 volts and presumably that's what the motor saw, but I doubt it given the leads.  The current was 14.3 amps, which calculates to 186 watts.

Test B: Battery @ 13.5v and current @ 14.5 amps for 196 watts.

And I'll tell you, the air flow in the cab was night and day different to what I've been getting!  There's nothing wrong with the blower motor that a little bit more juice wouldn't solve.

So now I'm going to be checking the wiring.  I thought I put a relay in the ground circuit, but if so I must not have wired it correctly.  And I certainly need a relay in the power feed.  

[85lebaront2]

Gary, inside the cab, near the HVAC inlet, is a pretty healthy connector, should be brown, if yours isn't partially melted I will be surprised. It carries the blower ground side connections to the switch. Also take a good look at the blower switch plug and the two lead underhood plug for the blower motor. All of these will typically show heat damage.

Basically check every plug in the blower circuit for signs of being overheated and clean or replace them.

For some reason Ford decided to use the ground side for speed selection (like Chrysler) unlike GM who used the power side and then a big relay with a 30 amp in-line fuse off the alternator for high.

[Gary Lewis]

Thanks, Bill.  But I'm not really wanting to fix the existing wiring since the wires are small and long and the connectors are many - although I did check them when I did the transformation.  Instead I want relays to give full power to the motor at all times when the ignition is on, and a relay to give a solid ground when in High.

I thought I was there on the ground side because I have Relay #5 in the passenger's side PDB, as shown below.  But that isn't working as there's a ground on the O/BK going to the motor if the blower control is in High, even when the key is off.  Or even when #5 is pulled out of the PDB.  So I have a problem there.

And that drawing is wrong since I no longer use Relay #1 to trigger the starter and am using the fender-mounted relay instead.  So my plan is to use #1 to provide power to the motor and #5 for the ground in High.  That should give me full battery voltage at the motor.

As for the connector under the hood, that's where I broke into the system.  I've made pins to insert into the female side by cutting 1/4" male terminals down to fit and then I'm jumpering to the male connector.  So I know it is clean.

So, what do you think of that plan?

[85lebaront2]

Ok, one relay to get direct power to the O blower motor wire (+) and the other to ground the B blower motor wire (becomes O/BK) in high. Since you are re doing all of that wiring, I would look into using terminal 30 on the ground side relay as the ground pin, 87a to ground the switch and 87 to ground the blower motor. That way you can eliminate some of the present connectors. I may at some point mess with the HVAC wiring on Darth, but the 1996 system is so greatly improved it may not be needed.

[Gary Lewis]

I'm with you for all of that but the "87a to ground the switch" bit.  Can you say that another way?

I've simplified the page from the 85 EVTM to remove everything that doesn't apply to Big Blue and am preparing to add the relays.  I deleted the text that explains how the HVAC system works, which gives me room to work.

[ArdWrknTrk]

Now you understand why I installed the E450 fan relay kit I got from U-haul parts online.
It sits inside the passenger fender just clear of the hood hinge and jack.
Came with adhesive heat shrink crimps already installed.

Edit: it takes power directly from the input bus connection of my little fuse & relay box, through a 30A inline fuse holder to the blower motor.

[85lebaront2]

Gary, the idea is to move the ground side of the switch to a solid underhood ground, probably right at the battery. 87a is connected to 30 with the relay de-energised so if the switch ground is through it it will have the same ground as the Hi setting. It would just be 1 more wire from switch to relay box.

[Gary Lewis]

Jim - Yes, I understand why.  For sure.  Luckily I have two relay spots in the PDB so I can use those spots and make the blower HUMMM!

Jim - I'm still not 100% sure I understand.  From what I'm looking at I only have to break into two wires, as shown below.  The top one is to supply power and the bottom one is to supply the ground, but only when the switch goes to High.

I'll try to map out what you are saying, but I don't want to run any wires to the switch.  From what I'm seeing I just need 30 and 87 on the ground relay and let the current go through the resistors for the lower speeds.  But I'm sure I'm missing something.

[ArdWrknTrk]

Your truck was setup as W/Euraspark... correct?

Yeah, the orange wire triggers the relay, that I grounded through the mounting screw to the fender.
The relay gets power from the Megafuse connection, through an inline fuse holder, and provides power to the blower motor in all positions but 'off'.

You don't need to relay the ground side.(but you could)
261 is heavy enough to handle the blower easily.
Run a dedicated ground wire to 701, like I did with my audio upgrade, and run an overlay ground past Splices 802 & 165 from the speed selector switch.

I find it interesting that G106 is connected all the time to the resistor.
Didn't we have a user puzzling why they had one fan speed (low) that never shut off?
And no high or intermediate speeds?

[Gary Lewis]

Euraspark?  I don't recognize that term, but then it is a new year.  So please refresh my memory.

As for the ground relay, I already have it, although it isn't wired quite right.  So I just need to sort that out and I'll have the ground relay that will fix that voltage drop problem - and take a load off the switch itself.

I should have posted my cleaned up version of that schematic instead of the very busy one from the '85 EVTM.  In any case, your comment about G106 clicked and now I see what Bill is saying - run Ckt 57 to the ground relay and use 87A to ground it.  But then you'd lose the ground to the AC clutch when the blower is in high and the relay is picked.  (I'm not sure Big Blue is wired that way but will check it out when I'm "in there".)

As for someone with only Low and it won't shut off, I've slept since then and don't remember that very clearly.  But that would take two problems: The function switch would have to feed power even in the off position, and either the blower would have to be bad or G701 bad.  Right?

But Rene's high-only problem could be due to a blown thermal limiter or a bad G106.  Does that make sense?

[ArdWrknTrk]

Dollars to donuts he's popped the thermal fuse, unless someone left the wire off.
They are easily available for replacement in coffee makers and irons.

Show me 106 from the grounds page of the 85 EVTM.

[Gary Lewis]

Yes, I think it is the thermal limiter as well.  And I told him so but he's not responded.

Good catch on G106.  Had never gone looking for it.  And it doesn't show in the 81 or 86 EVTM either.  

And how 'bout that G701 for the blower motor switch?  It seems to be somewhat well used.  Might be good to get a high-current device like the blower off of it.

[ArdWrknTrk]

Gary Lewis wrote

Euraspark?  I don't recognize that term, but then it is a new year.  So please refresh my memory

(A) I was in the truck. (B) On my phone.(C) Without my glasses. (D) It was early, before my 4th coffee. (E) all the above.

The schematic shows EEC & Duraspark.
You have extensively modified BB's harness, but I don't know (or care) exactly how.

I'll go look for the thread since it is germane, or this conversation is germane to IT....

[Gary Lewis]

Now I see said the blind man.  But 4 cuppas?  You must be drinking low-test as my 2 cups of Starbucks "gets my motor running" so I can "head out on the highway".

I suppose I have EEC since I'm running the EEC-V system.

[ArdWrknTrk]

No, I'm a caffeine addict with high resistance.
I should literally just buy the powdered caffeine and sniff it to stay awake in the flatbed.

I meant of the 2 diagrams you posted which is closest to what's actually going on?

Alright, here's the thread.  https://forum.garysgaragemahal.com/Heater-Air-Flow-is-always-low-tp143525.html

[Gary Lewis]

I now see why I didn't remember much of that thread as it was while I was traveling.  You probably noticed that I was in and out and didn't have much contribution nor context.

But in the end he seems to have the fan on all the time, even in the OFF position.  That would seem to say that he has a bad function switch.  Or maybe the wrong function switch as there were some changes along the way.  But it is supposed to be the function switch that gives the motor power or not.

As for the diagrams, I don't know which is the most accurate.  But I hope to nail down exactly how it is wired, at least in that area, and document it as I work through this.

Janey and I've talked and we want to take the trip to SW Okiehoma in February, so I have time to tear into the PDB and get this sorted - and documented.

[Ifitaintbroke]

[ArdWrknTrk]

Gary Lewis wrote

And how 'bout that G701 for the blower motor switch?  It seems to be somewhat well used.  Might be good to get a high-current device like the blower off of it.

G701 has almost everything in the harness tied to it.
The tank senders are at the rear, and brought up there.

That's why I made a dedicated ground from 701 and brought it to what would have been my EEC ground that's part of the - terminal of my battery clamp.
It was easy to run while I was getting power and relay for the tiny 8" sub under my seat.

[Gary Lewis]

I've not changed G701 or added another ground to it, but I did ensure it is making good electrical contact with the cab.  And I have made absolutely sure that the cab is well and truly grounded to the battery.  But it wouldn't hurt to add a jumper from it to another grounding point.  

We've had doctor's appointments yesterday and today, so I've done nothing on this.  But I hope to get started tomorrow.

[ArdWrknTrk]

I've seen your grounding scheme and have to say it's a far sight better than stock!  

You could probably add a jumper from 701 to any of your added cab grounds.

I have to remain conscious of the braided strap between the pinch* weld below my driver's floor and the left cab support getting corroded.

I'm just pointing out what I've done, and how it improved the blower situation in my truck.

(I have a new screen protector and it's VERY FRUSTRATING 😖)